In casings used for vehicle-mounted electronic control units or the like, the compatibility between a characteristic in which it is preferable to block the communication between the inside and the outside of a casing (for example, water-proofness or dust-proofness), and a characteristic achieved by permitting the communication between the inside and outside of the case (for example, permeability for preventing occurrence of the pressure differential between the inside and the outside) is required. Under such a request, resin molded products including a gas permeable membrane that blocks water droplets, oil droplets, and dusts but permits ventilation are suggested (see Patent Documents 1, 2, and 3).
The technique of Patent Document 1 (JP-A-2003-152347) solves a problem of a gas permeable sheet being easily damaged because a gas permeable sheet (gas permeable membrane) is exposed to the outside or the like as in a connector case (a resin molded product) of the conventional art. That is, as shown in FIG. 12 of the present application, a casing member (a lid 2 of Patent Document 1) according to claim 1 of Patent Document 1 includes a casing member main body (a lid main body 10 in Patent Document 1) having a first ventilation hole H0, a gas permeable sheet S, and a cover member C1 that has its peripheral edge portion airtightly bonded to the casing member in order to protect the gas permeable sheet S. The cover member C1 is formed with a second air passage hole H1 having a smaller diameter than that of the first air passage hole H0. Also, one ventilation path that extends through the casing member main body in its thickness direction (that is, a direction along the central axis of the first air passage hole H0) is constructed by the first air passage hole H0, the gas permeable sheet S, and the second air passage hole H1. In addition, according to FIGS. 5 to 7 of Patent Document 1, a molding die used for manufacturing the casing member (the lid 2) is constituted by a lower mold (cavity mold F1 in Patent Document 1) that holds the cover member C1, and an upper mold (a core mold F2 in Patent Document 1) that forms a cavity with the lower mold when the mold is closed. The upper mold is able to be brought close to or separated from the lower mold in a vertical direction.